The present invention relates generally to optical scanning systems. More particularly, this invention relates to a scanning system having a large depth of field which is capable of focusing on and scanning a plurality of targets over a wide range of distances.
Coded symbologies are being used in a vast array of applications. The ability to track a large amount of items quickly and efficiently has led coded symbologies to be used in applications such as retail checkout, warehousing, inventory control and document tracking. As the volume of items tracked by coded symbologies has increased, the need for optical scanners which operate at high speeds has likewise increased.
Various optical scanning systems have been developed for reading and decoding coded symbologies. Such optical scanning systems typically incorporate a non-coherent light source and a light detecting means, such as a CMOS- or CCD-based image sensor. A portion of the light which is reflected from the coded symbology is detected by the image sensor and converted into an electrical signal, which is the basis for the digital image of the coded symbology that has been scanned. The digital image is then processed and decoded according to the specific type of coded symbology.
One disadvantage with all current CMOS- and CCD-based scanning systems is that they require a mechanical focusing apparatus in order to focus the light reflected from the coded symbology onto the image sensor. Since a mechanical focusing apparatus typically operates slower than the image sensor and other electronics within the scanner, the focusing apparatus tends to be the limiting factor in the speed of operation of the scanning system. Although there are scanning systems that are available which do not require a moveable focusing apparatus, these scanning systems typically have a very small depth of field.
Accordingly, there exists a need for an efficient and inexpensive scanning system that can accurately read and decode coded symbologies over a large depth of field without requiring a moving mechanical apparatus to focus light on the image sensor.
The present invention is a scanning system which utilizes a randomly addressable CMOS area array sensor which is selectively positioned at the Scheimpflug angle in the image plane in order to detect focused light reflected from an object. Light reflected from the object is focused onto the CMOS area array sensor through an objective lens. Since the CMOS area array sensor is mounted at the Scheimpflug angle, each strip within the depth of field of the object plane has a corresponding string of pixels on the CMOS area array sensor which are in focus. The system may include a means for determining the distance between the scanner and the object. Once the distance between the scanner and the object is determined, the system reads out only those pixels which are in focus.
Objects and advantages will become apparent to those skilled in the art after reading the detailed description of a presently preferred embodiment.